1. Field of the Invention
The present invention generally relates to electrical cables, and more particularly to electrical cable strain reliefs and methods of manufacture thereof.
2. Background Information
Strain reliefs are used in generally all electrical components which have power cords needing to be plugged into a wall receptacle. These power cords typically extend through an opening in the case or housing of the component. If left unprotected, the power cord would soon fray due to the friction of rubbing against the case opening.
A first purpose of a strain relief is to protect the electrical cord from rubbing against the edges of the opening. A second purpose of a strain relief is to relieve bending strains in the cord as it bends at or near its connection with the opening.
FIG. 1 and FIG. 2 show a common type of prior art strain relief. This type strain relief has a threaded first piece 2 which is typically fastened to the body of the appliance through use of a threaded nut (not shown). This first piece 2 has an extended compression ring through which the wire 5 is inserted. The threaded second piece 4 of the strain relief is then threaded on and compresses the compression ring against the wire. This works reasonably well except in heavy duty applications, such as in commercial vacuum cleaners.
The problem is that as the wire and the threaded strain relief are continuously pulled, twisted and flexed, the compression ring is working fixedly against the power cord, and eventually will start to fray and break the metal strands within the wires within the cord. When this occurs, it will eventually result in a dead short and the heat from the short will melt the threaded strain relief.
A second type of prior art strain relief is used on some lighter duty appliances. These strain reliefs are a single piece which is directly molded on the cord. They are formed by placing the wire cord in a jig, closing up the jig, and injecting PVC to directly bond the strain relief to the outer jacket of the electric cord. However, this is not done with threaded ends because the material is not strong enough to hold a threaded end. This type of direct, injected strain relief is typically used on thin, plastic cases for appliances where the soft cord has a washer-like protrusion on the end which fits into notches between two halves of the case that are then later joined together.
What is needed is a strain relief which overcomes the shortcomings of the prior art. The present invention serves this purpose.
The present invention is a two-part strain relief. At one end is a threaded end which is hard, preferably glass-filled nylon, which is slid over the cord. The threaded end has two flanges attached to it, and has holes in its shaft so that when direct molded PVC (or other pliable material) is later injected, the PVC will go through the holes and encase the two flanges thereby holding the threaded end tightly bonded to the flexible PVC end.
With this new type of strain relief, there is no compression of the cord, and as a result its life expectancy is significantly greater. The hard threaded end is amenable for use in a variety of applications, from extending through a hole in a metal container, and more importantly, through a hole in a rotational molded container where the thickness of the roto-molded container case wall can vary substantially from part to part, thus necessitating the use of a threaded end.
A first embodiment of the present invention is a method of making a strain relief for protecting a cord extending through the strain relief. This method comprises first inserting the cord through a plug portion. This plug portion having a passageway therethrough extending generally along its axis. This plug portion also has a first end and a second end, with at least one port extending through the plug portion to the passageway near the second end. Second, a mold is placed around at least a portion of the plug portion. Third, a formed piece is created by injecting a plastic material into the mold so as to form a jacket around at least a portion of the plug portion. This jacket covering the second end of the plug portion, and preferably extending through the port(s) into the passageway and around the portion of the cord extending through the portion passageway. It is preferred that the jacket further extending outwards from the second end, parallel to the cord. Finally, the mold would be removed from the formed piece.
A second embodiment of the present invention is an apparatus, namely a strain relief for protecting a cord extending through a housing. This strain relief comprises a plug portion, a fitting portion and a molded jacket. The plug portion has a cord receiving orifice extending therethrough, wherein the cord extends through the cord receiving orifice. The fitting portion is adapted fix the plug portion on a housing. The molded jacket attaches to a portion of the plug portion with a central orifice which surrounds the cord. It is preferred that the plug portion and the fitting portion be threaded. It is preferred that the plug portion comprise at least one port extending from an outside surface of the plug portion to the cord receiving orifice, wherein the molded jacket further extends through the port and into the cord receiving orifice. It is also preferred that the molded jacket comprise a material which is more pliable than the material comprising the plug portion, for instance the molded jacket could be comprised of polyvinyl chloride (PVC) plastic, and the plug portion could be comprised of glass-filled nylon.
A third embodiment of the present invention is an apparatus, namely a strain relief for protecting the cord of an electrical component from fraying and other damage, such an electrical component having a housing through which the cord extends. The strain relief has a generally cylindrical plug portion, an attachment means for attaching said plug portion to said housing, and a jacket molded onto said plug portion. The plug portion has a passageway therethrough extending generally along the axis of the cylindrical plug portion. The plug portion has a first end and a second end. The plug portion contains at least one port extending from an exterior surface of the plug portion to the passageway near the second end. The jacket covers the plug portion second end, extending through the ports, into the passageway, and around the cord extending through the plug portion passageway. The jacket further extends outwards from the second end, parallel to the cord. It is preferred that the first end be threaded, and that the attachment means be a threaded nut. It is preferred that the plug portion further comprise at least one protuberance extending out from the plug portion near the second end. One type of such a protuberance comprises at least one retainer band circumscribing the plug portion near the second end, the molded jacket molded around the band. It is also preferred that the molded jacket comprise a material which is more pliable than the material comprising the plug portion, for instance, the molded jacket could be comprised of polyvinyl chloride (PVC) plastic, and the plug portion could be comprised of glass filled nylon.
In a fourth embodiment, the apparatus is a strain relief for protecting the cord of an electrical component from fraying, such an electrical component having a housing through which the cord extends. In such an embodiment, the strain relief would comprise an elongated plug portion, a threaded fitting and a jacket molded onto said plug portion. The preferred plug portion having a passageway extending longitudinally therethrough. The plug portion having a first end and a second end, wherein the first end is threaded, and wherein at least one retainer band circumscribes the plug portion near the second end. The threaded fitting being adapted to thread onto the plug portion at the plug portion first end. The jacket covering the plug portion second end, said jacket further encasing the retainer band. The jacket further extending outwards from the second end, parallel to the cord, and defining a passage for the cord and surrounding the cord. It is also preferred that the molded jacket comprise a material which is more pliable than the material comprising the plug portion, for instance the molded jacket could be comprised of polyvinyl chloride (PVC) plastic, and the plug portion could be glass filled nylon.
Still other objects and advantages of the present invention will become readily apparent to those skilled in this art from the following detailed description wherein I have shown and described only the preferred embodiment of the invention, simply by way of illustration of the best mode contemplated by carrying out my invention. As will be realized, the invention is capable of modification in various obvious respects all without departing from the invention. Accordingly, the drawings and description of the preferred embodiment are to be regarded as illustrative in nature, and not as restrictive.